Self sharpening polycrystalline diamond compact with high impact resistance

ABSTRACT

A polycrystalline diamond compact for use in cutting operations with a renewable sharp cutting edge, high abrasion resistance and high impact strength. The polycrystalline diamond is a composite composed of a matrix of coarse diamond interspersed with large agglomerated particles of ultra fine diamond. The agglomerated particles produce sharp cutting edges that are protected from impact forces by the overall uniform matrix of coarse diamond crystals. The self-sharpening cutter is highly resistant to spalling and catastrophic fracture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sintered polycrystalline diamondcomposite for use in rock drilling, machining of wear resistant metals,and other operations which require the high abrasion resistance or wearresistance of a diamond surface. Specifically, this invention relates topolycrystalline diamond which has been sintered at high temperatures andhigh pressure with the aid of a catalyst to form strong diamond todiamond bonding.

2. Description of the Art

Composite polycrystalline diamond compacts or PCD have been used forindustrial applications including rock drilling and metal machining formany years. One of the factors limiting the success of the PCD is thegeneration of heat due to friction between the PCD and the workmaterial. This heat causes thermal damage to the PCD in the form ofcracks which lead to spalling of the polycrystalline diamond layer,delamination between the polycrystalline diamond and substrate, and backconversion of the diamond to graphite causing rapid abrasive wear.

When the PCD cutter is new, it generally has a circular geometry, and itthus presents a sharp cutting edge to the work material. However, afteruse for some time, this circular or arc-shaped cutting edge wears into astraight flat surface that cannot as effectively penetrate the workmaterial. When used for rock drilling, the worn PCD cutter acts as afriction bearing surface that generates heat, which accelerates the wearof the PCD cutter and slows the penetration rate of the drill. FIG. 1shows a wear flat generated on a prior art cutter at location 1.

Prior art methods to solve this problem, such as discussed in U.S. Pat.No. 4,784,023 to Dennis, utilize a substrate with a non-planar surfaceso that the interface between the diamond and the substrate isirregular. The result is a diamond layer which has both thin and thicksections. The thicker portion of the polycrystalline diamond offers moreabrasion resistance and wears at a slower rate. Failure analysis ofdrill bits containing PCDs with non-planar interfaces shows that theworn cutting edges of the cutters are irregular and sharper than thoseof cutters made with planar interfaces. Although this has generally beenshown to be an improvement, there is still an area of concern. Whennon-planar substrates are used, highly localized stress occurs at theinterface, causing cracking which can result in catastrophic failure ofthe cutter.

In U.S. Pat. No. 4,784,023, the disadvantage of using relatively fewparallel grooves with planar side walls is that the stress becomesconcentrated along the top and, more importantly, the base of eachgroove and results in significant cracking of the metallic substratealong the edges of the bottom of the groove. This cracking significantlyweakens the substrate whose main purpose is to provide mechanicalstrength to the thin polycrystalline diamond layer. As a result,construction of a polycrystalline diamond cutter following the teachingsprovided by U.S. Pat. No 4,784,023 is not suitable for cuttingapplications where repeated high impact forces are encountered, such asin percussive drilling; nor is it suitable in applications where extremethermal shock is a consideration. FIG. 2 shows a prior art cutter ofthis design and the location of cracking at edges 3.

Other configurations have been proposed in order to overcome problems ofstress in the compact due to the mismatch in thermal expansion betweenthe diamond layer and the tungsten carbide substrate. For example, U.S.Pat. No. 5,351,772 describes the use of radially extending raised landson one side of the tungsten carbide substrate area on which apolycrystalline diamond table is formed and bonded.

U.S. Pat. No. 5,011,616 describes a substrate with a surface topographyformed by irregularities having non-planar side walls, such that theconcentration of substrate material continuously and gradually decreasesat deeper penetrations into the diamond layer. U.S. Pat. No. 5,379,854describes a substrate with a hemispherical interface between the diamondlayer and the substrate, the hemispherical interface containing ridgesthat penetrate into the diamond layer. U.S. Pat. No. 5,355,969 describesan interface between the substrate and polycrystalline layer defined bya surface topography with radially-spaced-apart protuberances anddepressions.

All of the above proposals show a diamond layer of varying thicknessrelative to the surface of the tungsten carbide substrate support. Thus,in areas where the diamond layer is thicker, the amount of cobaltavailable is less than in those areas where the diamond layer is thin.This results in a non-uniformly sintered diamond layer thatsubstantially weakens the compact. Even when cobalt powder is pre-mixedwith the diamond prior to subjecting the compact to high pressure-hightemperature conditions, the presence of cobalt in a substrate with atextured surface produces areas of varying concentration of cobaltwithin the diamond layer during the sintering process and causes softspots or poorly sintered areas within the diamond layer.

It has been proposed to use transitional layers to better sinter thediamond and improve the adhesion of the polycrystalline diamond to thesubstrate.

One of the solutions to these problems is proposed in U.S. Pat. No.4,604,106. This PCD utilizes one or more transitional layersincorporating powdered mixtures with various percentages of diamond,tungsten, carbide, and cobalt to distribute the stress caused by thedifference in thermal expansion over a larger area. A problem with thissolution is that the cobalt cemented carbide in the mixture weakens thatportion of the diamond layer because less diamond-to-diamond directbonding occurs as a result of the carbide second phase.

U.S. Pat. No. 4,311,490 teaches the use of coarse diamond particles nextto the tungsten support with a layer of finer diamond particles placedon top as the exposed cutting surface. This is reported to reduce theoccurrence of soft spots or poorly sintered areas in the diamond tablesince the coarser particles have larger channels between them, making iteasier for cobalt to sweep through the diamond nearest the tungstencarbide substrate, thus allowing thicker diamond layers to be sintered.For rock drilling applications, however, it has been found that althoughfiner diamond results in higher abrasion resistance, it also results insignificantly less impact resistance. The lower impact resistanceproduces compact cutter failure by way of fracturing and spalling of thediamond layer from the tungsten carbide support substrate.

U.S. Pat. No. 5,645,617 also uses layers of diamond with differentaverage particle sizes.

The problem with the layer designs is that they do not provide a meansto cause irregular wear of the cutting edge and thus do not eliminatethe problem of formations of a relatively large wear flat. Thus, itwould be useful to have a means to control the geometry of the cuttingedge and at the same time limit the stress caused by using non-planarinterfaces.

U.S. Pat. No. 5,855,996 shows a polycrystalline diamond compact whichincorporates different sized diamond. Specifically, it describes mixingsubmicron sized diamond particles together with larger sized diamondparticles in order to create a more densely packed compact by fillingthe interstices between the larger diamond with diamond particles ofsmaller size. The problem with this approach is that the uniformly densediamond PCD produces a uniformly flat, dull working surface at thecutting interface. The dull edge thus created as the PCD wears slows thepenetration rate in rock drilling applications, creates heat, and cracksonce initiated proceed unhindered across the entire PCD layer.

U.S. Pat. No. 6,187,068 B1 teaches the separation of diamond intolaterally spaced regions of discrete particle size areas. Thepolycrystalline diamond areas formed of the finer size diamond particlesprovide a higher abrasion resistance and a slower wear rate, thusproviding a non-linear cutting edge. The problem with this solution isthat the areas of different diamond size are relatively large in sizeand do not provide a sharp enough cutting edge as wear progresses. Thus,although offering an improvement over other geometries, heat is stillgenerated at the working surface. Additionally, the large geometricpatterns of differing particle sizes produce stress along the boundariesbetween the discrete particle size areas leading to catastrophicfracture of the polycrystalline material. FIG. 3 shows a cross sectionof a prior art cutter of this design. Cracking occurs at the edgeboundaries 4 and 5 between the different geographic areas.

SUMMARY OF THE INVENTION

The instant invention is to uniformly distribute an aggregate of finediamond particles throughout a matrix of larger sized diamond particles.The aggregates are sized to perform as single large grains of very highabrasion resistance distributed in a matrix constructed of somewhatsmaller diamond single crystals.

The overall composite polycrystalline diamond performs as a blend ofvarious size diamond crystals sintered together wherein the largestgranules are actually blocky shaped structures composed of fine diamondsingle crystals. Thus, there are no continuous edge boundaries alonglarge geometric shaped areas of discrete particle sizes. The result isthat much sharper cutting edges form as the polycrystalline materialwears, and long fracture lines do not occur along boundaries between thedifferent geographic areas. Impact failure occurs by chipping ratherthan spalling of large areas or catastrophic cracking.

BRIEF DESCRIPTION OF THE DRAWING

The various features, advantages, and other uses of the presentinvention will become more apparent by referring to the followingdetailed description and drawing, in which:

FIG. 1 is a perspective view of one prior art polycrystalline diamondcompact;

FIG. 2 is a perspective view of a second prior art polycrystallinediamond compact;

FIG. 3 is a perspective view of a prior art polycrystalline diamondcompact with discrete particle size areas,

FIG. 4 is shows an enlarged cross sectional view of one embodiment ofthis invention;

FIG. 5 shows a second embodiment of this invention supported by asubstrate;

FIG. 6 shows a third embodiment of this invention supported by asubstrate with a non-planar interface;

FIG. 7 shows a fourth embodiment of this invention formed over asubstrate with a curved surface;

FIG. 8 shows an enlarged photograph of a prior art wear flat; and

FIG. 9 shows an enlarged photograph of a wear surface generated by thecutter illustrated in FIG. 5.

DETAILED DESCRIPTION

In the following description, it should be understood that the compositedescribed hereafter as formed of polycrystalline diamond, PCD, orsintered diamond as the material is often referred to in the art, canalso be any of the super hard abrasive materials, including, but notlimited to, synthetic or natural diamond, cubic boron nitride, andwurzite boron nitride, as well as combinations thereof.

FIG. 4 shows an enlarged cross sectional view of one embodiment of thisinvention which includes a polycrystalline diamond matrix 6 withaggregates 7 composed of ultra fine diamond particles. The matrix ismade up of an aggregate of fine diamond particles distributed throughouta matrix of larger diamond wherein the matrix is made up of particleswhose average diameter is at least five times larger than the diamondcomponent of the aggregate. The interstices 8 between the diamondcrystals in the matrix are filled with catalyst material or can be voidif the catalyst is removed by acid leaching or other methods.

FIG. 5 shows a second embodiment of this invention. In this embodiment,the polycrystalline composite is a layer supported by a substrate 9 toform a compact or cutting element.

The substrate 9 is preferably formed of a hard metal. In a specificexample, the substrate 9 is formed of a metal carbide selected from thegroup consisting of a tungsten carbide, titanium carbide, tantalumcarbide, and mixtures thereof The substrate 9 may also be formed of acarbide from the group of IVB, VB, or VIB metals which is pressed andsintered in the presence of a binder of cobalt, nickel, iron, and alloysthereof

In FIG. 5, the interface 10 between the polycrystalline diamond area 11and the substrate 9 has a planar or flat configuration. In a thirdembodiment depicted in FIG. 6, the substrate 12 is formed with aplurality of equally spaced, generally parallel grooves to form thediamond/carbide interface 13. The grooves may be straight sided orformed with angled side walls which are disposed at acute or obliqueangles with respect to the plane of substrate 12. Other nonflat surfaceirregularities may also be employed at the interface 13. Interfaces withany of the other surface topographies known in the art may also beemployed.

FIG. 7 shows a fourth embodiment of this invention. In this embodiment,the polycrystalline composite is formed over a substrate 14 with acurved surface 15.

FIG. 8 shows an enlarged photograph of a wear flat generated by a priorart PDC cutter. FIG. 9 shows an enlarged photograph of the sharp wearsurface generated by a PDC cutter made according to this invention.

EXAMPLE #1

A 1 gram sample of 0.4 micron diamond powder was processed and sieved toobtain blocky agglomerated grains between 250 microns and 600 microns insize. A 100 milligram sample of the sieved blocky grains was then mixedwith 400 milligrams of 25 micron diamond powder. The diamond mixture wasthen placed into a molybdenum cup. Finally, a cobalt cemented tungstencarbide substrate was placed into the cup on top of the diamond powder.This assembly was then loaded into a high pressure cell and pressed to45 K-bars for fifteen minutes at 1450° C. After cutting the power to thecell and allowing the cell to cool at high pressure for one minute, thepressure was released. The composite bodies were removed from the othercell components and then lapped and ground to final dimension.

The abrasion resistance of this cutter was measured after machiningBarre granite. This value was in excess of 2 times the abrasionresistance of a standard PDC. Additionally, the noise and vibration ofthe machining operation was significantly reduced over that of astandard PDC.

EXAMPLE #2

A 1 gram sample of 0.4 micron diamond powder was processed and sieved toobtain blocky agglomerated grains between 250 microns and 600 microns insize. A 100 milligram sample of the sieved blocky grains was then mixedwith 400 milligrams of a blend of diamond ranging in size from 2 micronsto 30 microns. The average particle size of the blend was about 20microns. The diamond mixture was then placed into a molybdenum cup.Finally, a cobalt cemented tungsten carbide substrate was placed intothe cup on top of the diamond powder. This assembly was then loaded intoa high pressure cell and pressed to 45 K-bars for fifteen minutes at1450° C. After cutting the power to the cell and allowing the cell tocool at high pressure for one minute, the pressure was released. Thecomposite bodies were removed from the other cell components and thenlapped and ground to final dimension.

The impact resistance of this cutter was compared to that of a standardPDC. The breakage of this cutter was through small chipping of the PDCdiamond layer at point of impact verses spalling of larger areas of PDCdiamond on the standard PDC cutter.

1. A polycrystalline diamond composite comprising: aggregations of finediamond particles distributed throughout a matrix of larger diamondparticles wherein the matrix is made up of particles whose averagediameter is at least five times larger than the diameter of the diamondcomponent particles of the aggregations.
 2. The composite of claim 1wherein the diamond is supported by a cobalt cemented tungsten carbidesubstrate.
 3. The composite of claim 1 wherein a catalyst used to sinterthe composite has been removed from the composite.
 4. The composite ofclaim 1 wherein a catalyst used to sinter the composite has beenrendered in-operative.
 5. The composite of claim 1 wherein theaggregations comprise diamond powder with an average particle size lessthan 1 micron and the matrix diamond has an average particle size lessthan 30 microns.
 6. The composite of claim 1 wherein the averagediameter of the aggregations is larger than 100 microns.
 7. Thecomposite of claim 1 wherein the average diameter of the aggregations isbetween 250 microns and 500 microns.
 8. The improvement of claim 1further comprising: a substrate formed of a hard metal.
 9. Theimprovement of claim 8 wherein the substrate is formed of a metalcarbide selected from the group consisting of a tungsten carbide,titanium carbide, tantalum carbide, and mixtures thereof.
 10. Theimprovement of claim 8 wherein the substrate is formed of a carbide fromthe group of IV, V, VB a VIB metals.
 11. The improvement of claim 10wherein the carbide is pressed and sintered in the presence of a binderof at least one colbalt, nickel, iron, and alloys thereof.
 12. Theimprovement of claim 8 wherein an interface between the substrate andthe polycrystalline diamond has a planar configuration.
 13. Theimprovement of claim 8 wherein an interface is formed of a plurality ofspaced, substantially parallel grooves in at least one of the substrateand the polycrystalline diamond.
 14. The improvement of claim 13 whereinthe grooves are formed of spaced sidewalls extending from a bottom wall.15. The improvement of claim 14 wherein the sidewalls are disposed at anon-perpendicular angle with respect to the bottom wall.